Internal combustion engines are used in a variety of applications, such as lawn mowers, generators, pumps, snow blowers, and the like. Such engines often have carburetors wherein fuel received from a fuel source is mixed with air and supplied to a combustion chamber for ignition. The fuel mixture is drawn from the carburetor into the combustion chamber due to a low pressure created in the combustion chamber by the rotation of the engine. The products of combustion are then expelled from the combustion chamber into the exhaust manifold during the exhaust stroke of the engine.
An operator of an engine may shut the engine down by grounding the electrical ignition system, thereby causing the spark plug to cease firing. After shutdown, the engine does not immediately stop rotating. During the continued rotation or coasting of the engine after ignition shutdown, unburned fuel and air are drawn from the carburetor into the combustion chamber, and expelled into the exhaust system.
The continued draw of unburned fuel into the combustion chamber and exhaust manifold after engine shutdown causes problems. Fuel is wasted, and unburned fuel is released into the environment, thereby increasing exhaust emissions. Additionally, the muffler or muffler with catalytic converter often get very hot, and the unburned fuel may ignite when it contacts these components, thereby causing backfiring or afterburning. Backfiring and afterburning can shorten the useful life of the catalytic converter and of the muffler itself. Likewise, the presence of unburned fuel in the combustion chamber may cause dieseling.
To alleviate these problems, fuel shutoff mechanisms have been devised to control the flow of fuel after ignition shutdown. For instance, U.S. Pat. No. 5,301,644 to Olmr discloses a fuel shutoff mechanism which includes a solenoid valve. However, the '644 system, as well as other apparatus which use solenoids, typically require a battery to function. The addition of a battery to engines adds to the weight and cost of the engine. Additionally, solenoids, or other electric actuating devices, are expensive and are expensive to replace. In the small utility engine industry, for example, the additional cost, weight, and complexity are very undesirable.
Other fuel shutoff devices, such as the one disclosed in U.S. Pat. No. 5,092,295 to Kobayashi, use the throttle of the engine to act as a fuel blocker upon engine shutdown. This is done by adding structure which overrides the governor of the engine and closes the throttle valve upon shutdown. The problem with these devices, however, is that they are complex, and must be added onto and may disturb the delicate balance of the engine governor.
Yet other devices, such as U. S. Pat. No. 4,510,739 to Dluhosch, use a fuel shutoff valve which stops the flow of fuel into the fuel bowl. The disadvantage of these devices is that a substantial amount of fuel remains in the fuel bowl after the engine ignition is shut down, and can still be drawn into the combustion chamber and exhaust system after shutdown.